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              <p class="caption" role="heading"><span class="caption-text">第一章 初始化</span></p>
<ul>
<li class="toctree-l1"><a class="reference internal" href="Ch1-0%20%E5%87%86%E5%A4%87%E5%B7%A5%E4%BD%9C.html">Ch1-0 准备工作</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch1-1%20%E5%88%9B%E5%BB%BAGLFW%E7%AA%97%E5%8F%A3.html">Ch1-1 创建GLFW窗口</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch1-2%20%E5%88%9D%E5%A7%8B%E5%8C%96%E6%B5%81%E7%A8%8B.html">Ch1-2 初始化流程</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch1-3%20%E5%88%9B%E5%BB%BAVK%E5%AE%9E%E4%BE%8B%E4%B8%8E%E9%80%BB%E8%BE%91%E8%AE%BE%E5%A4%87.html">Ch1-3 创建VK实例与逻辑设备</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch1-4%20%E5%88%9B%E5%BB%BA%E4%BA%A4%E6%8D%A2%E9%93%BE.html">Ch1-4 创建交换链</a></li>
</ul>
<p class="caption" role="heading"><span class="caption-text">第二章 绘制一个三角形</span></p>
<ul>
<li class="toctree-l1"><a class="reference internal" href="Ch2-0%20%E4%BB%A3%E7%A0%81%E6%95%B4%E7%90%86%E5%8F%8A%E4%B8%80%E4%BA%9B%E8%BE%85%E5%8A%A9%E7%B1%BB.html">Ch2-0 代码整理及一些辅助类</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch2-1%20Rendering%20Loop.html">Ch2-1 Rendering Loop</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch2-2%20%E5%88%9B%E5%BB%BA%E6%B8%B2%E6%9F%93%E9%80%9A%E9%81%93%E5%92%8C%E5%B8%A7%E7%BC%93%E5%86%B2.html">Ch2-2 创建渲染通道和帧缓冲</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch2-3%20%E5%88%9B%E5%BB%BA%E7%AE%A1%E7%BA%BF%E5%B9%B6%E7%BB%98%E5%88%B6%E4%B8%89%E8%A7%92%E5%BD%A2.html">Ch2-3 创建管线并绘制三角形</a></li>
</ul>
<p class="caption" role="heading"><span class="caption-text">第三章 纵观Vulkan</span></p>
<ul>
<li class="toctree-l1"><a class="reference internal" href="Ch3-1%20%E5%90%8C%E6%AD%A5%E5%8E%9F%E8%AF%AD.html">Ch3-1 同步原语</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch3-2%20%E5%9B%BE%E5%83%8F%E4%B8%8E%E7%BC%93%E5%86%B2%E5%8C%BA.html">Ch3-2 图像与缓冲区</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch3-3%20%E7%AE%A1%E7%BA%BF%E5%B8%83%E5%B1%80%E5%92%8C%E7%AE%A1%E7%BA%BF.html">Ch3-3 管线布局和管线</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch3-4%20%E6%B8%B2%E6%9F%93%E9%80%9A%E9%81%93%E5%92%8C%E5%B8%A7%E7%BC%93%E5%86%B2.html">Ch3-4 渲染通道和帧缓冲</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch3-5%20%E5%91%BD%E4%BB%A4%E7%BC%93%E5%86%B2%E5%8C%BA.html">Ch3-5 命令缓冲区</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch3-6%20%E6%8F%8F%E8%BF%B0%E7%AC%A6.html">Ch3-6 描述符</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch3-7%20%E9%87%87%E6%A0%B7%E5%99%A8.html">Ch3-7 采样器</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch3-8%20%E6%9F%A5%E8%AF%A2.html">Ch3-8 查询</a></li>
</ul>
<p class="caption" role="heading"><span class="caption-text">第四章 着色器</span></p>
<ul class="current">
<li class="toctree-l1"><a class="reference internal" href="Ch4-1%20%E7%9D%80%E8%89%B2%E5%99%A8%E6%A8%A1%E7%BB%84.html">Ch4-1 着色器模组</a></li>
<li class="toctree-l1 current"><a class="current reference internal" href="#">Ch4-2 顶点着色器</a><ul>
<li class="toctree-l2"><a class="reference internal" href="#id1">顶点着色器的内置输入</a></li>
<li class="toctree-l2"><a class="reference internal" href="#id2">顶点着色器的内置输出</a><ul>
<li class="toctree-l3"><a class="reference internal" href="#gl-position">gl_Position</a></li>
<li class="toctree-l3"><a class="reference internal" href="#gl-clipdistance">gl_ClipDistance</a></li>
<li class="toctree-l3"><a class="reference internal" href="#gl-culldistance">gl_CullDistance</a></li>
</ul>
</li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="Ch4-3%20%E7%89%87%E6%AE%B5%E7%9D%80%E8%89%B2%E5%99%A8.html">Ch4-3 片段着色器</a></li>
</ul>
<p class="caption" role="heading"><span class="caption-text">第五章 封装常用对象</span></p>
<ul>
<li class="toctree-l1"><a class="reference internal" href="Ch5-0%20VKBase%2B.h.html">Ch5-0 VKBase+.h</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch5-1%20%E5%90%84%E7%A7%8D%E7%BC%93%E5%86%B2%E5%8C%BA.html">Ch5-1 各种缓冲区</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch5-2%202D%E8%B4%B4%E5%9B%BE%E5%8F%8A%E7%94%9F%E6%88%90Mipmap.html">Ch5-2 2D贴图及生成Mipmap</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch5-3%202D%E8%B4%B4%E5%9B%BE%E6%95%B0%E7%BB%84.html">Ch5-3 2D贴图数组</a></li>
</ul>
<p class="caption" role="heading"><span class="caption-text">第六章 进阶Vulkan</span></p>
<ul>
<li class="toctree-l1"><a class="reference internal" href="Ch6-0%20%E4%BD%BF%E7%94%A8%E6%96%B0%E7%89%88%E6%9C%AC%E7%89%B9%E6%80%A7.html">Ch6-0 使用新版本特性</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch6-1%20%E6%97%A0%E5%9B%BE%E5%83%8F%E5%B8%A7%E7%BC%93%E5%86%B2.html">Ch6-1 无图像帧缓冲</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch6-2%20%E5%8A%A8%E6%80%81%E6%B8%B2%E6%9F%93.html">Ch6-2 动态渲染</a></li>
</ul>
<p class="caption" role="heading"><span class="caption-text">第七章 基础示例</span></p>
<ul>
<li class="toctree-l1"><a class="reference internal" href="Ch7-1%20%E5%88%9D%E8%AF%86%E9%A1%B6%E7%82%B9%E7%BC%93%E5%86%B2%E5%8C%BA.html">Ch7-1 初识顶点缓冲区</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch7-2%20%E5%88%9D%E8%AF%86%E7%B4%A2%E5%BC%95%E7%BC%93%E5%86%B2%E5%8C%BA.html">Ch7-2 初识索引缓冲区</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch7-3%20%E5%88%9D%E8%AF%86%E5%AE%9E%E4%BE%8B%E5%8C%96%E7%BB%98%E5%88%B6.html">Ch7-3 初识实例化绘制</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch7-4%20%E5%88%9D%E8%AF%86Push%20Constant.html">Ch7-4 初识Push Constant</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch7-5%20%E5%88%9D%E8%AF%86Uniform%E7%BC%93%E5%86%B2%E5%8C%BA.html">Ch7-5 初识Uniform缓冲区</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch7-6%20%E6%8B%B7%E8%B4%9D%E5%9B%BE%E5%83%8F%E5%88%B0%E5%B1%8F%E5%B9%95.html">Ch7-6 拷贝图像到屏幕</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch7-7%20%E4%BD%BF%E7%94%A8%E8%B4%B4%E5%9B%BE.html">Ch7-7 使用贴图</a></li>
</ul>
<p class="caption" role="heading"><span class="caption-text">第八章 简单示例</span></p>
<ul>
<li class="toctree-l1"><a class="reference internal" href="Ch8-1%20%E7%A6%BB%E5%B1%8F%E6%B8%B2%E6%9F%93.html">Ch8-1 离屏渲染</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch8-2%20%E6%B7%B1%E5%BA%A6%E6%B5%8B%E8%AF%95%E5%92%8C%E6%B7%B1%E5%BA%A6%E5%8F%AF%E8%A7%86%E5%8C%96.html">Ch8-2 深度测试和深度可视化</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch8-3%20%E5%BB%B6%E8%BF%9F%E6%B8%B2%E6%9F%93.html">Ch8-3 延迟渲染</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch8-4%20%E9%A2%84%E4%B9%98Alpha.html">Ch8-4 预乘Alpha</a></li>
<li class="toctree-l1"><a class="reference internal" href="Ch8-5%20sRGB%E8%89%B2%E5%BD%A9%E7%A9%BA%E9%97%B4%E4%B8%8E%E5%BC%80%E5%90%AFHDR.html">Ch8-5 sRGB色彩空间与开启HDR</a></li>
</ul>
<p class="caption" role="heading"><span class="caption-text">附录</span></p>
<ul>
<li class="toctree-l1"><a class="reference internal" href="Ap1-1%20%E8%BF%90%E8%A1%8C%E6%9C%9F%E7%BC%96%E8%AF%91GLSL.html">Ap1-1 运行期编译GLSL</a></li>
</ul>

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  <section id="ch4-2">
<h1>Ch4-2 顶点着色器<a class="headerlink" href="#ch4-2" title="Permalink to this heading"></a></h1>
<p>
    顶点着色器（vertex shader）是图形管线中的一个着色器，它可以处理来自顶点缓冲区的数据，或根据一定的规则直接生成顶点数据。
    <br>
    若非Task/Mesh管线，那么顶点着色器是图形管线中最初执行的着色器。
</p>
<p>
    顶点着色器逐顶点发生调用。
</p><section id="id1">
<h2>顶点着色器的内置输入<a class="headerlink" href="#id1" title="Permalink to this heading"></a></h2>
<p>
    用GLSL编写的顶点着色器有以下内置输入：
</p>
<table class="docutils align-default">
    <colgroup>
        <col style="width: 30%" />
        <col style="width: 70%" />
    </colgroup>
    <thead>
        <tr class="row-odd">
            <th class="head" colspan="2"><p>全局变量</p></th>
        </tr>
    </thead>
    <tbody>
        <tr class="row-even">
            <td><p><span class="kw">int</span> gl_VertexIndex</p></td>
            <td><p>表示当前顶点的索引</p></td>
        </tr>
        <tr class="row-odd">
            <td><p><span class="kw">int</span> gl_InstanceIndex</p></td>
            <td><p>表示当前实例的索引</p></td>
        </tr>
        <tr class="row-even">
            <td><p><span class="kw">int</span> gl_DrawID</p></td>
            <td><p>在多重绘制或间接绘制命令中，表示当前绘制的索引</p></td>
        </tr>
        <tr class="row-odd">
            <td><p><span class="kw">int</span> gl_BaseVertex</p></td>
            <td><p>表示本次绘制中的起始顶点索引</p></td>
        </tr>
        <tr class="row-even">
            <td><p><span class="kw">int</span> gl_BaseInstance</p></td>
            <td><p>表示本次绘制中的起始实例索引</p></td>
        </tr>
    </tbody>
</table>
<p>
    对于非索引绘制命令，比如<code><a href="https://renderdoc.org/vkspec_chunked/chap21.html#vkCmdDraw">vkCmdDraw</a>(commandBuffer, vertexCount, instanceCount, firstVertex, firstInstance)</code>，gl_BaseVertex值为firstVertex，gl_VertexIndex必然不小于该值，类似地，gl_BaseInstance值为firstInstance，gl_InstanceIndex必然不小于该值。
<p>
</p>
    对于索引绘制命令，比如<code><a href="https://renderdoc.org/vkspec_chunked/chap21.html#vkCmdDrawIndexed">vkCmdDrawIndexed</a>(commandBuffer, indexCount, instanceCount, firstIndex, vertexOffset, firstInstance)</code>，gl_BaseVertex值为vertexOffset，gl_VertexIndex为命令缓冲区中的与firstIndex相应的索引值加上vertexOffset。
</p>
<p>
    从OpenGL转来的程序员注意gl_InstanceIndex语义同gl_InstanceID不同（gl_InstanceID从0开始，不计算gl_BaseInstance）。
    <br>
    gl_DrawID是从OpenGL所使用的GLSL继承而来的，因此不写作gl_DrawIndex。
</p></section>
<section id="id2">
<h2>顶点着色器的内置输出<a class="headerlink" href="#id2" title="Permalink to this heading"></a></h2>
<p>
    用GLSL编写的顶点着色器有以下内置输出：
</p>
<table class="docutils align-default">
    <colgroup>
        <col style="width: 30%" />
        <col style="width: 70%" />
    </colgroup>
    <thead>
        <tr class="row-odd">
            <th class="head" colspan="2"><p>预定义块gl_PerVertex 的成员</p></th>
        </tr>
    </thead>
    <tbody>
        <tr class="row-even">
            <td><p><span class="type">vec4</span> gl_Position</p></td>
            <td><p>顶点位置</p></td>
        </tr>
        <tr class="row-odd">
            <td><p><span class="kw">float</span> gl_PointSize</p></td>
            <td><p>点的大小，适用于绘制点</p></td>
        </tr>
        <tr class="row-even">
            <td><p><span class="kw">float</span> gl_ClipDistance[]</p></td>
            <td><p>自定义剪裁参数</p></td>
        </tr>
        <tr class="row-odd">
            <td><p><span class="kw">float</span> gl_CullDistance[]</p></td>
            <td><p>自定义剔除参数</p></td>
        </tr>
    </tbody>
</table>
<ul>
    <li>
        <p>
            所有的输出都是可选的，非必须输出。
        </p>
    </li>
    <li>
        <p>
            gl_PerVertex意味着这些输出是相对于每个顶点而言的，gl_PerVertex是没有实例名称的预定义块，意味着你不需要使用任何前缀就可以直接使用它的成员，即直接写<code>gl_Position</code>而不是写<code>gl_PerVertex.gl_Position</code>。
        </p>
    </li>
</ul><section id="gl-position">
<h3>gl_Position<a class="headerlink" href="#gl-position" title="Permalink to this heading"></a></h3>
<p>
    gl_Position与片段渲染在屏幕上的位置及深度值的关系参见<a class="reference internal" href="Ch4-1%20%E7%9D%80%E8%89%B2%E5%99%A8%E6%A8%A1%E7%BB%84.html#id4">NDC坐标</a>。
    <br>
    如果顶点着色器之后只有一个片段着色器，或没有任何着色器（旨在不输出颜色，只输出深度值到片段所在位置），应当输出gl_Position（若是连gl_Position都不必输出的情形，必是纯粹的计算和数据存储，应使用//TODO Ch4-6 计算着色器）。
    <br>
    gl_Position在栅格化时发生插值，插值方式考虑透视（即相当于<a class="reference internal" href="Ch4-1%20%E7%9D%80%E8%89%B2%E5%99%A8%E6%A8%A1%E7%BB%84.html#id11">插值修饰符</a>为<span class="kw">smooth</span>）。
</p></section>
<section id="gl-clipdistance">
<h3>gl_ClipDistance<a class="headerlink" href="#gl-clipdistance" title="Permalink to this heading"></a></h3>
<p>
    gl_ClipDistance数组中的每个元素代表着到不同剪裁平面的距离。
    <br>
    “剪裁”的效果大致等价于：对于任意片段，若gl_ClipDistance数组中的任一元素数值小于0，则该片段被丢弃。
    <br>
    上述只是一种直观且便于理解的解释，因为<strong>这里所谓的剪裁发生在栅格化前</strong>，其底层实现可能是修改图元，并不需要涉及片段。
</p>
<p>
    <strong>剪裁可能会生成新的顶点</strong>，例如：
    <br>
    若三角形有一个角被裁掉，会生成两个新的顶点构成新的边，变成一个四边形（即两个三角形图元）。
    <br>
    （该行为的结果影响<a class="reference internal" href="Ch3-8%20%E6%9F%A5%E8%AF%A2.html#id7">管线统计</a>）
</p>
<p>
    要使用gl_ClipDistance，需开启<a class="reference internal" href="Ch1-3%20%E5%88%9B%E5%BB%BAVK%E5%AE%9E%E4%BE%8B%E4%B8%8E%E9%80%BB%E8%BE%91%E8%AE%BE%E5%A4%87.html#device_feature">设备特性</a>中的shaderClipDistance，gl_ClipDistance数组元素个数最大不超过硬件限制中的maxClipDistances。
</p>
<p>
    利用gl_ClipDistance在3D渲染中将模型切开：
</p>
<img alt="_images/ch4-2-2.png" src="_images/ch4-2-2.png" width="360px">
<ul>
    <li>
        <p>
            用例：有一种简单粗暴的渲染镜面效果的方法——将物体沿着镜面翻转然后再渲染一遍，典型的情况比如渲染物体在水面上的倒影，倒影当然只会映照出水面以上的物体，利用gl_ClipDistance即可轻易地达成这一效果。
        </p>
    </li>
</ul>
<p>
    绘制三角形的三条边（图元类型为三角形，绘制模式为<span class="enum">VK_POLYGON_MODE_LINE</span>），令gl_ClipDistance[0]为gl_Position.x的效果如下：
</p>
<img alt="_images/ch4-2-1.png" src="_images/ch4-2-1.png">
<ul>
    <li>
        <p>
            在英伟达显卡上你可能会看到中央被截断的地方也构成了一条边，那是硬件特定的行为。
        </p>
    </li>
</ul></section>
<section id="gl-culldistance">
<h3>gl_CullDistance<a class="headerlink" href="#gl-culldistance" title="Permalink to this heading"></a></h3>
<p>
    gl_CullDistance数组中的每个元素代表着到不同剔除平面的距离，则：
    <br>
    对于任意图元，若构成其图形的所有顶点皆满足到某一剔除平面的距离小于0（比如gl_CullDistance[0]都小于0），则图元被整个丢弃。
</p>
<p>
    要使用gl_CullDistance，需开启<a class="reference internal" href="Ch1-3%20%E5%88%9B%E5%BB%BAVK%E5%AE%9E%E4%BE%8B%E4%B8%8E%E9%80%BB%E8%BE%91%E8%AE%BE%E5%A4%87.html#device_feature">设备特性</a>中的shaderCullDistance，gl_CullDistance数组元素个数最大不超过硬件限制中的maxCullDistances。
</p></section>
</section>
</section>


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